The heat pump is the name commonly applied in present commercial practice to a year-round air-conditioning system employing refrigeration equipment in a manner which enables a surface to deliver usable heat to a space during the winter period and to abstract heat from the space during the summer. When operating the heating system, the cooling coils, or evaporator, absorb heat from an outside medium and deliver it, together with a heat equivalent of the work of compression, to the condenser, which in turn gives it up to the space to be heated. On the other hand, when operating as a cooling system, the evaporating coils absorb heat from the conditioned space, and reject it, together with the heat equivalent with the work of compression, to the outside medium. There is no fundamental difference between the heat pump and a conventional refrigeration system. Thermodynamically both systems are heat pumps employing a compressor, condenser, cooling coils, and expansion valve to absorb heat at a low-temperature level and reject it at a higher-temperature level. The idea of an apparatus comprising the basic heat pump has been well-known since the time of Lord Kelvin and has been widely employed in both industrial and residential applications.
The four basic-type heat pump systems for building heating and cooling most commonly employed are: (1) air to air, in which air is used as the source of heat and air is used to remove the heat from the condenser; (2) water to air, in which water is used as the heat source and air is used to remove the heat from the condenser; (3) air to liquid, in which air is used as the source of heat and liquid is used to transfer the heat from the condenser and chiller; and (4) water to water, in which water is used as the heat source and water is used to transfer the heat from the condenser and chiller. The application described herein is addressed to the air to air type system, which is the most common type employed in residential applications. However, as will become apparent upon further reading of the present specification, the present invention is equally applicable to other type systems.
Reversing or switchover valves are employed in heat pump systems to receive refrigerant from the compressor and to selectively divert it to either the indoor or outdoor heat exchanger coils, dependent upon the system mode (heating or cooling) of operation. The valve simultaneously operates to communicate the suction port of the compressor with the coil not presently connected to the compressor outlet.
Numerous reversing valve designs are disclosed in the patent literature. Although enjoying varying degrees of commercial success, most prior art devices have a number of shortcomings. Typically, an externally mounted three-way control valve is employed to modulate a larger spool valve. In addition to being expensive, this arrangement proves to be vulnerable to damage by requiring external plumbing for fluidly interconnecting the control and spool valves. A related problem resides in this arrangement's inherent bulkiness and packaging difficulty with other components in a heat pump system. Many reversing valves are touted as having all metal construction within extemely close tolerances. Although functional, such devices often prove to be extremely expensive due to the large number of high precision machining operations required as well as the enhanced difficulty in manufacture and assembly. Finally, many prior art valves require high force actuators to ensure positive operation. Such actuators can substantially increase electrical power consumption and thereby reduce overall system operating efficiency as well as to slow response time of the valve.